You can buy a TAP card:

Attention Metrolink Riders

Your 1-Way/Roundtrip, Weekend Pass, 7-Day Pass and Monthly Metrolink passes enable you to board Metro Rail or Metro buses to complete your commute. Metrolink tickets with a TAP and EZ transit pass logo are accepted as a flash pass and require visual inspection onboard buses. Metrolink passes that have an EZ transit pass logo are eligible to ride as base fare on all Metro Bus, Metro Rapid Lines and Metro Rail routes. Customers with Metrolink tickets must have a separate TAP card with stored value to pay for Express or Silver Line upcharges: Full Fare $0.75 or Senior/Disabled $0.60.

Many educational institutions and businesses throughout the region offer group-rate TAP cards to their students and employees. Check with your school’s business office or your workplace’s Employee Transportation Coordinator to see if group-rate TAP cards are available.